Touch sensor systems, such as touchscreens or touch monitors, can act as input devices for interactive computer systems used for various applications, for example, information kiosks, order entry systems, video displays, mobile communications, etc. Such systems may be integrated into a computing device, thus providing interactive touch capable computing devices, including computers, electronic book readers, or mobile communications devices.
Generally, touch sensor systems enable the determination of a position on the surface of a substrate via a user's touch of the surface. The touch substrate is typically made of some form of glass which overlies a computer or computing device display, like a liquid crystal display (LCD), an organic light emitting diode (OLED) display, plasma display, etc. The touch sensor system is operatively connected to the device display so as to enable the determination of a position on the device display and, moreover, of the appropriate control action of a user interface such as shown on the display.
Touch sensor systems may be implemented using different technologies. Acoustic touch sensors, such as ultrasonic touch sensors using surface acoustic waves, are currently one of the dominant touch sensor technologies and different types of acoustic touch sensors now exist. For example, an “Adler-type” acoustic touch sensor uses only two transducers per coordinate axis to spatially spread a transmitted surface acoustic wave signal and determines the touch surface coordinates by analyzing temporal aspects of a wave perturbation from a touch. For each axis, one transducer at a respective peripheral surface generates surface acoustic wave pulses that propagate through the substrate along a perpendicular peripheral surface along which a first reflective grating or array is disposed. The first reflective array is adapted to reflect portions of a surface acoustic wave perpendicularly across the substrate along plural parallel paths to a second reflective array disposed on the opposite peripheral surface. The second reflective array reflects the surface acoustic wave along the peripheral surface to a second transducer where the wave is received for processing. The reflective arrays associated with the X axis are perpendicular to the reflective arrays associated with the Y axis so as to provide a grid pattern to enable two-dimensional coordinates of a touch on the substrate to be determined. Touching the substrate surface at a point causes a loss of energy by the surface acoustic waves passing through the point of touch. This is manifested as an attenuation of the surface acoustic waves and is detected by the receiving transducers as a perturbation in the surface acoustic wave signal. A time delay analysis of the data is used to determine the surface coordinates of a touch on the substrate.
An acoustic touch sensor may have a large number of operative elements (either multiple transducers, or transducer and reflective array combinations) disposed on, and along, the front peripheral surfaces of the substrate. In order to prevent damage due to exposure from the environment or external objects, the housing for these sensors or for the devices integrating a sensor may include a bezel for the front peripheral surfaces of the touch substrate that hides and protects these peripheral operative elements, so that only an active touch region on the front surface of the substrate is exposed for possible touch input. For bezel-less acoustic touch sensors, the peripheral operative elements may be located on the back peripheral surfaces of the substrate (in this case, a surface acoustic wave propagates around a substrate edge, across the front surface, and around the opposite substrate edge to reach the receiving elements). Thin-width bezel and bezel-less acoustic touch sensors each seek to maximize the active touch region, which may be beneficial for small-sized integrated devices, like a smartphone, a tablet computer, an electronic book reader, or other mobile computing device.
As the active touch region enlarges, more device features and touch functions may be provided in the active touch region. In some cases, however, these additional features and functions may interfere with the propagation of surface acoustic waves on the touch substrate. For example, in many bezel-less systems that have certain aesthetic considerations, the periphery of the back surface of the substrate may have a generally acoustically benign layer (“border layer”), which may be an opaque layer of paint or ink applied on a border region of the surface, with the peripheral operative elements being bonded or printed on top of the “border layer” so that the elements are hidden from view through the typically transparent substrate.
It may be desired in some applications to provide in the border layer on the border region an area without paint or ink in order to provide a camera window or acoustic hole (i.e., an unobstructed optical path from a camera lens disposed behind the substrate, through the substrate, to the outside of the device) for an integrated camera, which is one of the most desired device features. However, an attenuation or a dip in the surface acoustic wave signal at the receiving transducers may be observed at the location of the camera hole. Further, no touch response may be observed along a narrow band across the active touch region of the substrate centered at the camera hole.
The aforementioned problems are addressed by the present invention according to specific embodiments.